Technique to Determine Water Uptake in Organic Plots

Core Ideas Measurement and theory were combined to determine evapotranspiration.Uncertainty was considered for evapotranspiration determination.Input included meteorological, crop, and minimal soil properties. Methods to determine crop water use may be difficult to implement on numerous research plots. The purpose of this study was to calculate Priestley‐Taylor evapotranspiration (ET) from measured input and to assess uncertainty. Input data included net radiation, air temperature, barometric pressure, green ground cover, total ground cover, the ratio of crop to total green cover, soil texture class, and clay content for each soil layer, and periodic water content measurements with depth (daily for soil surface). The relationship between seasonal water use and yield was similar to literature values for alfalfa (Medicago sativa L.) and oat (Avena sativa L.) dry matter as well as for soybean [Glycine max (L.) Merr.] grain yield, but the calculated water use was lower (∼80%) than literature values for corn (Zea mays L.) grain yield. Monthly trends in water use reflected the seasonal crop growth. In summary, the proposed technique was useful across multiple plots and cropping treatments, and was more reliable than a water balance approach in areas with lateral and upward flow due to periodic high water tables.